Data from: Pyoverdin cheats fail to invade bacterial populations in stationary phase

Microbes engage in cooperative behaviours by producing and secreting public goods, the benefits of which are shared among cells, and are therefore susceptible to exploitation by nonproducing cheats. In nature, bacteria are not typically colonizing sterile, rich environments in contrast to laboratory experiments, which involve inoculating sterile culture with few bacterial cells that then race to fill the available niche. Here, we study the potential implications of this difference, using the production of pyoverdin, an iron-scavenging siderophore that acts as a public good in the bacteria Pseudomonas aeruginosa. We show that (1) nonproducers are able to invade cultures of producers when added at the start of growth or during early exponential growth phase, but not during late exponential or stationary phase; (2) the producer strain does not produce pyoverdin in the late exponential and stationary phases and so is not paying the cost of cooperating during those phases. These results suggest that whether a nonproducing mutant can invade will depend upon when the mutation arises, as well as the population structure, and raise a potential difficulty with the use of antimicrobial treatment strategies that propose to exploit the invasive abilities of cheats.微生物通过合成并分泌公共物品（public goods）来实施合作行为，这类公共物品的收益可在细胞间共享，因此极易被不生产该物品的欺骗型突变体（cheats）所利用。与实验室实验场景不同，自然环境中的细菌通常不会定植于无菌且营养丰富的环境中——实验室实验一般是将少量细菌细胞接种至无菌培养基内，随后细菌会快速增殖以占据所有可利用的生态位。本研究以铜绿假单胞菌（Pseudomonas aeruginosa）中的pyoverdin（一种夺铁型嗜铁素，作为该菌的公共物品）的合成为研究模型，探讨上述实验与自然环境差异可能带来的研究启示。本研究证实：其一，若在生长初期或早期指数生长期接种不产pyoverdin的欺骗型突变体，该菌株可入侵产pyoverdin菌株的培养体系，但在晚期指数生长期或稳定期接种则无法实现入侵；其二，产pyoverdin菌株在晚期指数生长期及稳定期并不会合成pyoverdin，因此在该阶段无需承担合作所需的代谢成本。上述研究结果表明，不产公共物品的突变体能否实现入侵，取决于突变发生的时机以及种群结构；同时本研究也指出，一类试图利用欺骗型突变体入侵能力的抗菌治疗策略，可能存在潜在的应用难题。